Inks for use on digital duplicators and stencil duplicators are generally based on water-in-oil emulsions, although the use of non-emulsion inks is also known. Examples of conventional water-in-oil emulsion inks are disclosed in U.S. Pat. No. 5,378,739.
JP-A-6,128,516 discloses a water-in-oil emulsion ink for use in a stencil printing method and which has improved set-off properties. The ink includes a thermosetting or a hot-melting component in the oil phase and a siliccone oil in the aqueous and/or oil phase in an amount of 1 to 20% w/w based on the total ink. In the inks exemplified the amount of silicone oil in the oil phase is at most 21.6% w/w.
A disadvantage with such inks is that their consumption level is dependent upon temperature, and consequently they give varying print quality depending on the temperature of the operating environment. Aspects of print quality which relate to ink consumption, and therefore ink temperature, include print density, set-off and solid area infill.
EP-A-0,661,356 discloses a water-in-oil emulsion ink said to have improved temperature dependence. The ink contains a water-insoluble colouring agent in the aqueous phase thereby avoiding the need for a resinous dispersing agent in the oil phase. While a degree of temperature independence is achieved, this is only significant at the lower end of the normal operating range, and not over the whole range.